"For the longest time Canonical has slapped an LTS moniker on some of their Ubuntu releases. Currently, a new major release of the operating system happens every six months, and is supported for 18 months after release. Whereas in the past when LTS versions received two years support or more, the current model - starting with 12.04 - supports new LTS releases for five years. However, a recent public Google Hangouts session revealed that Canonical has been thinking about switching from the venerable LTS model to a rolling release, starting with version 14.04."

I don't think Google would choose the 'most unstable Linux distribution out there' as their GoogleOS.
I use Ubuntu most of the time and I honestly think it's currently the best free user experience out there. As a power user you might like better this or that distro, but for the common person, Ubuntu is as stable, polished and well integrated a desktop can be. I've met a few Mac zealots who converted to Ubuntu and in my book, that means quite a bit.